May 1, 1908] 



SCIENCE 



699 



complex and little-understood factors, rather 

 than with a few simple ones. 



In my book I therefore attempted, by cita- 

 tion of precise experimental data, to show the 

 great number of factors which play a part in 

 determining behavior; to show that changes in 

 the internal system which makes up the organ- 

 ism are of equal importance for this, with 

 changes in the external system which makes up 

 the environment; and I set forth particularly 

 those remarkable relations of dependence and 

 support between the acts of behavior and the 

 other physiological processes, that are com- 

 monly spoken of as adaptation. 



4. My positive contention that behavior in 

 the lower organisms is complex, varied and 

 variable, so that it is not easily predictable, led 

 me to a criticism of theories which represented 

 such behavior as simple, uniform over wide 

 fields, and unequivocally determined by single 

 external factors. I found a theory of this 

 character to be widely held ; I met it in opposi- 

 tion at every turn as my papers began more 

 and more to present behavior as complex; and 

 I found this view presented regularly under 

 the name of the " tropism theory." 



This then was the reason for my attack on 

 the tropism theory. I criticized it, not as a 

 mere statement of one of the factors that make 

 up the complex phenomena of behavior, but as 

 a view of supposed extremely wide applica- 

 bility, which maintained the simplicity and 

 uniformity of the behavior of the lower organ- 

 isms. I tried to show that there was no single 

 schema into which most of the behavior of the 

 lower organisms could be forced. How far it 

 was just to identify the view criticized with 

 the tropism theory we shall inquire in a mo- 

 ment; here it is most important, if we wish 

 to get a clear understanding of the grounds of 

 apparent conflict, to grasp the fact that the 

 simplicity, uniformity and general application 

 of a single schema were the points against 

 which my criticism was directed. 



Was this idea of the tropism theory suffi- 

 ciently general to justify a criticism of it on 

 that basis? The word tropism has been used 

 in many senses and the theory has taken many 

 forms, as we shall see later; but I believe that 

 any one who has followed the literature of 



behavior must realize that there was such 

 justification, even though he may himself hold 

 to some other definition of the word tropism. 

 The great movement toward extreme simpli- 

 fication in these matters has certainly been 

 generally identified with the tropism theory; 

 " reduction to simple tropisms " has been the 

 ideal. Doubtless not all investigators have 

 held the tropism theory to be so simple and of 

 such wide applicability, but it is true that 

 there has been a general belief that such was 

 the case — a belief not confined to the unin- 

 formed, but shared by workers of high stand- 

 ing. Thus, Bohn, in his recent admirable re- 

 view' of this entire question, after setting 

 forth in detail examples of the tropism theory, 

 says, " It is evident that nothing is simpler 

 than this explanation," and again, " For more 

 than ten years certain biologists have thus 

 explained the actions of animals by tropisms. 

 . . . This had become the necessary and suf- 

 ficient explanation of all cases. Whenever it 

 was observed that animals accumulated at a 

 point, without even seeking to determine how 

 they reached that point, a tropism was made 

 to intervene." Bohn makes these statements 

 merely as a presentation of well-known facts, 

 and it would be easy to multiply quotations 

 from biologists of the first rank showing that 

 this idea of tropisms was a general one. 



In view of certain passages in Professor 

 Loeb's recent paper,' a note of historical char- 

 acter is here required. My criticisms have 

 been directed not against any person or school, 

 but against a prevalent view. I have never 

 considered any single person as the sole author 

 or only proper expositor of the tropism theory, 

 but have taken the theory as I found it com- 

 monly presented in biological literature. I 

 have not, therefore, considered it necessary to 

 accompany a statement of my results with an 

 exposition of Loeb's work and views ; there are 

 other authors whose work and friendship I 

 value highly whose expressed views are more 

 directly in opposition with what I have 

 pointed out than are Loeb's. Certainly many 

 authors besides Loeb have ventured on inde- 



' Journal of Experimental Zoology, 4, 151-156. 



' " Les Tropismea, les ESfleies et I'lntelligence," 

 L'Annie Psychologique, T. 12, 1906, pp. 137-158. 



